1. Field of the Invention
The present invention relates to the field of image sensing devices and applications. More specifically, the present invention relates to a technology that combines fluorescent nano-particles (quantum dots) and methods to dispense and detect them for a range of optical tagging applications.
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2. Background Art
An increase in the awareness for security and fraud protection systems at many levels has created an influx in tagging applications in such fields as security/identification, counterfeit, ultra-high density data storage, manufacturing assembly, military, and civil remote sensing. Prior art tagging technologies are based on either bar-coding or radio frequency (RF). Technologies based on both bar-coding and RF have difficulties. Bar-code tags have to be manually scanned one at a time, and RF tags are at times difficult to introduce due to such handicaps as high volume/low cost, high tagging throughput of small parts, large number of combinations, and use with optical discs such as CDs and DVDs causing interference with the laser. This difficulty can be better understood with a review of prior art radio frequency identification (RDIF).
RDIF
RDIF is a means of identifying a person or an object using a radio frequency transmission, typically at 125 kHz, 13.56 MHz, or 800-900 MHz. RDIF has extensively been used in applications such as toll collection, access control, ticketing, and car immobilization devices. In recent years the technology has received an increased attention due to heightened security concerns and supply chain automation. Even though the primary benefit of RDIF tags over barcodes is their ease of use and reliability, RDIF tags cannot be placed on nano size objects or when a very high information density is required. PharmaSeq, Inc. and TAGSYS are two of the leading companies that use RDIF technology, but they both utilize circuits (about 0.25 mm) with radio frequency for applications mainly in the textile retail industry.
There is a need for an inexpensive alternative to barcode tags and for a nano sized alternative to RDIF tags. This alternative is a micro-fluidic device that controls small quantities of fluids by creating the equivalent of a vast network of large pumping circuitry with valves, combiners, splitters, and pumps onto an integrated chip. The components of the chip can be constructed from a multitude of different polymeric platforms that enable hydrodynamic control of fluid movement. FIG. 1 illustrates one such chip that incorporates micro-valves, pumps, and splitters that partitions a sample of fluid into three equal components for further analysis. The Figure has 4 separate blocks marked 1 through 4, which will be explained further below. The liquid sample is introduced with a syringe pump and fills the measuring channel until it reaches stopping valve A (block 1). The excess fluid is diverted through valve B (block 2). The fluid sample then proceeds through valve A and begins filling the dividing channels (block 3). Finally, block 4 shows three precisely measured, equal samples ready for further analysis.
FIG. 2 illustrates another prior art chip with an integrated mixer for three liquids. The flow of each channel is individually set to control the mixing ratio and perform simultaneous organic reactions in controlled ratios. In the Figure nitrophenylcarbonate is introduced in the chip at A. Three amines coming from the top of the chip at B, C, and D meet the nitrophenylcarbonate at microfluidic mixing junctions E, F, and G respectively. The mixtures are collected at exit ports (not shown) and confirmed using MS analysis. The Figure also shows, to the right, the chemical reaction between the nitrophenylcarbonate and the three amines. Certain fundamental properties of fluorescent liquid on a nano scale will better help in fully appreciating the present invention.
Fluorescent Liquid
Nanoliters volume of a liquid behaves very differently from liters volume of the same liquid. The effect of the guiding channels' walls become important at the nano scale because the walls tend to drag the liquid so that the center flows more rapidly than the edge. This characteristic could create a problem when different liquids are mixed to produce a homogeneous solution, especially organic liquids that tend to be sticky. However, chips made by several companies in the field overcomes this problem successfully.
For example, a homogenous solution created by mixing 39 different fluorescent quantum dots (QDs) each with 6 gray levels in a sub-micrometer spot size yields 1030 combinations (˜1000 bits/μm2). These QDs typically hold a few thousand atoms and are a few nanometers in diameter that selectively hold and release atoms. Since these QDs are composed of simple inorganic compounds making them chemically inert, and those with outer shells are stable to photochemical damage. Also, since the emission wavelength of a QD depends on its size, it is possible to tune the emission wavelength by controlling its size. The spectral linewidth may be as little as 12 nm at Full-Width Half-Maximum (FWHM) for a single nanocrystal. FIG. 3 illustrates an electron microscope image of a QD on the top. As seen in FIG. 3, the QD is about 10-15 nm across and consist of an inner core section 300 enclosed in a shell 310 which is covered in a polymer coating 320. The outermost layer is a streptavidin layer 330. The bottom of FIG. 3 illustrates a graph showing the typical absorbance and emission spectra of a typical QD with center wavelength 605 nm.